/*
 * Copyright 2014-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package de.codecentric.boot.admin.server.services;

import de.codecentric.boot.admin.server.domain.entities.Application;
import de.codecentric.boot.admin.server.domain.entities.Instance;
import de.codecentric.boot.admin.server.domain.values.BuildVersion;
import de.codecentric.boot.admin.server.domain.values.InstanceId;
import de.codecentric.boot.admin.server.domain.values.StatusInfo;
import de.codecentric.boot.admin.server.eventstore.InstanceEventPublisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.util.function.Tuple2;
import reactor.util.function.Tuples;

import java.time.Instant;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import javax.annotation.Nullable;

import static de.codecentric.boot.admin.server.domain.values.StatusInfo.STATUS_UNKNOWN;
import static java.util.Comparator.naturalOrder;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toMap;

/**
 * Registry for all applications that should be managed/administrated by the Spring Boot Admin
 * server. Backed by an InstanceRegistry for persistence and an InstanceEventPublisher for events
 *
 * @author Dean de Bree
 */
public class ApplicationRegistry {

    private final InstanceRegistry instanceRegistry;
    private final InstanceEventPublisher instanceEventPublisher;

    public ApplicationRegistry(InstanceRegistry instanceRegistry,
                               InstanceEventPublisher instanceEventPublisher) {
        this.instanceRegistry = instanceRegistry;
        this.instanceEventPublisher = instanceEventPublisher;
    }

    /**
     * Get a list of all registered applications.
     *
     * @return Flux of all the applications.
     */
    public Flux<Application> getApplications() {
        return this.instanceRegistry.getInstances()
                                    .filter(Instance::isRegistered)
                                    .groupBy(instance -> instance.getRegistration().getName())
                                    .flatMap(grouped -> toApplication(grouped.key(), grouped), Integer.MAX_VALUE);
    }

    /**
     * Get a specific application instance.
     * @param name the name of the application to find.
     * @return Mono with the application or an empty Mono if not found.
     */
    public Mono<Application> getApplication(String name) {
        return this.toApplication(name, this.instanceRegistry.getInstances(name).filter(Instance::isRegistered))
            .filter(a -> !a.getInstances().isEmpty());
    }

    public Flux<Application> getApplicationStream() {
        return Flux.from(this.instanceEventPublisher)
            .flatMap(event -> this.instanceRegistry.getInstance(event.getInstance()))
            .map(this::getApplicationForInstance)
            .flatMap(group -> toApplication(group.getT1(), group.getT2()));
    }

    public Flux<InstanceId> deregister(String name) {
        return this.instanceRegistry.getInstances(name)
                                    .flatMap(instance -> this.instanceRegistry.deregister(instance.getId()));
    }

    protected Tuple2<String, Flux<Instance>> getApplicationForInstance(Instance instance) {
        String name = instance.getRegistration().getName();
        return Tuples.of(name, this.instanceRegistry.getInstances(name).filter(Instance::isRegistered));
    }

    protected Mono<Application> toApplication(String name, Flux<Instance> instances) {
        return instances.collectList().map(instanceList -> {
            Tuple2<String, Instant> status = getStatus(instanceList);
            return Application
                .create(name)
                .instances(instanceList)
                .buildVersion(getBuildVersion(instanceList))
                .status(status.getT1())
                .statusTimestamp(status.getT2())
                .build();
        });
    }

    @Nullable
    protected BuildVersion getBuildVersion(List<Instance> instances) {
        List<BuildVersion> versions = instances.stream()
            .map(Instance::getBuildVersion)
            .filter(Objects::nonNull)
            .distinct()
            .sorted()
            .collect(toList());
        if (versions.isEmpty()) {
            return null;
        } else if (versions.size() == 1) {
            return versions.get(0);
        } else {
            return BuildVersion.valueOf(versions.get(0) + " ... " + versions.get(versions.size() - 1));
        }
    }

    protected Tuple2<String, Instant> getStatus(List<Instance> instances) {
        //TODO: Correct is just a second readmodel for groups
        Map<String, Instant> statusWithTime = instances.stream()
            .collect(toMap(instance -> instance.getStatusInfo().getStatus(),
                Instance::getStatusTimestamp,
                this::getMax
            ));
        if (statusWithTime.size() == 1) {
            Map.Entry<String, Instant> e = statusWithTime.entrySet().iterator().next();
            return Tuples.of(e.getKey(), e.getValue());
        }

        if (statusWithTime.containsKey(StatusInfo.STATUS_UP)) {
            Instant oldestNonUp = statusWithTime.entrySet()
                .stream()
                .filter(e -> !StatusInfo.STATUS_UP.equals(e.getKey()))
                .map(Map.Entry::getValue)
                .min(naturalOrder())
                .orElse(Instant.EPOCH);
            Instant latest = getMax(oldestNonUp, statusWithTime.getOrDefault(StatusInfo.STATUS_UP, Instant.EPOCH));
            return Tuples.of(StatusInfo.STATUS_RESTRICTED, latest);
        }

        return statusWithTime.entrySet()
            .stream()
            .min(Map.Entry.comparingByKey(StatusInfo.severity()))
            .map(e -> Tuples.of(e.getKey(), e.getValue()))
            .orElse(Tuples.of(STATUS_UNKNOWN, Instant.EPOCH));
    }

    protected Instant getMax(Instant t1, Instant t2) {
        return t1.compareTo(t2) >= 0 ? t1 : t2;
    }
}
